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Robots are teaching researchers a thing or two about rats, and rats about robots, in an unusual research program that has roboticists working alongside psychologists.

Very young rat pups have limited senses and motor skills, which make them excellent models for building simple robots and then comparing the machines to the real animals.

When roboticist Associate Professor Sanjay Joshi and psychologist Associate Professor Jeffrey Shank of the University of California at Davis did just that, they were surprised to discover new, unexpected behaviours emerging in both the robots and the rats.

"We program very simple rules for sensory-to-motor systems," says Joshi.

The robots they designed were larger versions of rat pups, about 30 centimetres long, and with similar pointed snouts.

The rat-bots also had sensors on their sides so they can feel their way around their pens the same way a seven to 10-day-old rat pup does before its eyes begin working.

"So the robot is a window into sensory development and motor development [of the rat pup]," says Joshi. "Ultimately we're interested in what the rat pup is thinking."

Following the rules

Among the rat-pup rules the rat-bots followed was to stay in touch with objects they encounter, usually the wall of their rectangular pen.

But when the robots were put into similar pens and allowed to roam, they did something unexpected: they bumped around the walls and then began favouring one wall.

Even more surprising is that a second look at the rat pups' behaviour revealed they were doing the same thing. But the researchers hadn't noticed it before.

The discovery is what's called an "emerging behaviour", since it was not programmed in, but comes about from an interaction with the real world.

That tells the researchers a lot about why the rat pups favour one wall and is a good sign that they programmed the rat-bots correctly.

Still, the rat-bots are a long way from being rat pups, Joshi says. For one thing, rats can bend their bodies, something the rat-bots can't yet do. And there are certain to be some complex behaviours that come from grouping robots together, as rat pups do.

"It allows us to test hypotheses about how animals are 'programmed'," says Assistant Professor Tucker Balch, a roboticist at Georgia Institute of Technology.